It is known for an object, such as a concretion, which is going to be destroyed by means of a lithotriptic apparatus, to be located in the body of a patient undergoing treatment by using ultrasonic waves. What is used for this purpose is an ultrasonic locating transducer such as a B-scanner.
The standard to which location can be accomplished with an ultrasonic locating transducer is generally satisfactory, provided the sound head of the said transducer is resting directly against the skin of the patient. If however this is not the case, it becomes considerably more difficult to locate the object to be destroyed. Due to the occurrence of multiple echoes and, due to the poor acoustic matching between the surface of the skin and the surface of the sound head, many of the ultrasonic waves are reflected at the skin and thus fail to impinge on the sound head. As a result there is considerable degradation of the image obtained from the signals received by the ultrasonic locating transducer.
This problem is particularly prevalent in lithotriptic apparatus in which the ultrasonic locating transducer is positioned in the ultrasonic shockwave transducer. As illustrations, reference may be made to certain embodiments disclosed in DE-OS 35 43 867 (U.S. Pat. No. 4,821,730).
Because of the cone of shockwaves transmitted from the ultrasonic shockwave transducer, it is not possible for the sound head of the locating transducer to be moved up close to the focus of the shockwave transducer. If it were, it would screen-off too much of the shockwave energy. Consequently, what happens is that the quality of the locating image obtained is degraded, as outlined above, especially when it is surface structures such as gall stones or salivary concretions or tumors close to the surface which are being located. Also, the distance from the sound head of the locating transducer to the body of the patient depends on the patient's build. Hence this distance will be greater with children and slim persons than with corpulent patients.
Hence, against the background outlined above, the object of the invention is to provide a remedy for these disadvantages. Therefore, and in particular, the aim is to produce an arrangement which, in known lithotriptic apparatus, will always ensure good ultrasonic location in the patient's body of the object to be destroyed without at the same time screening off therapeutic ultrasonic shockwaves.